Sophie Willis was attacked by Kaizer the dog in her home
A four-year-old girl needed 20 stitches to her face after she was savaged by her father's new dog.
Sophie Willis was attacked by the Rottweiler, named Kaizer, at her home in Cardiff.
Her father, Rob Willis, had bought Kaizer from Cardiff Council's dogs' home, on the city's Penarth Road, after it was picked up as a stray.
The dog has now been destroyed. A council spokesman said the dog had had a good temperament.
He added it had been walked by both adults and children during its two months at the home.
"We are of course extremely concerned to hear about the incident, which we understand happened when Kaizer was left alone with a young child, and wish the child a speedy recovery," he said.
Mr Willis, 47, who previously trained as a dog handler, said he bought the dog to work alongside him in his current job as a security guard.
The dog would then return home with him to Halliard Court, in Cardiff Bay, where he lives with his wife Caroline and two daughters - Sophie, and nine-year-old Rebecca.
Mr Willis said: "I took it on trust and the belief that the dog was going to be okay by what was said to us from the manager of the dog pound.
"The dog warden was there and there seemed to be a little bit of encouragement with regards to taking the dog on board.
"What I didn't expect was to leave the dog for five minutes for it then to savage my daughter."
He said he was "very upset" that his daughter could be scarred for life.
"I wish I could change everything - turn the clock back," he added.
The council spokesman said: "Kaizer had been at the dogs' home since February this year after being brought into the kennels as a stray.
"Although he was microchipped, staff had been unable to locate his previous owners as they had apparently moved on.
"He was used to being around people and had been walked by adults and children during his time at Cardiff dogs' home.
"He had a good temperament and had not given staff any cause for concern.
"His new owner informed us that he was a trained dog handler who wished to use the dog for his work as a security guard but that Kaizer would also be living in his family home.
"It seemed that Kaizer would meet his requirements and his new owner said he was pleased with the dog and would take it home."
The spokesman added that if a dog brought to the home was not deemed suitable for re-homing, for example, it is aggressive or in ill health, then it would be put to sleep on the advice of kennel staff or the vet.
The RSPCA said it recommended that small children were not left alone with any dog.
South Wales Police are currently consulting with the Crown Prosecution Service to establish what, if any, offences have been committed.